Functional fluid compositions

ABSTRACT

COMPOSITIONS WHICH INHIBIT AND CONTROL DAMAGE TO MECHANICAL MEMBERS IN CONTACT WITH SAID COMPOSITIONS WHICH COMPRISE CERTAIN HYDROCARBYL PHOSPHATE ESTER BASE STOCKS WHICH CONTAIN A DAMAGE INHIBITING AMOUNT OF AN ESTER OF THE STRUCTURE.   R-COO-R1

United States Patent Olfice US. Cl. 252-493 Claims ABSTRACT OF THE DISCLOSURE Compositions which inhibit and control damage to mechanical members in contact with said compositions which comprise certain hydrocarbyl phosphate ester base stocks which contain a damage inhibiting amount of an ester of the structure This application is a continuation-in-part of application Ser. No. 550,163, filed May 16, 1966, now abandoned.

This invention relates to functional fluid compositions having an ability to inhibit and control damage to mechanical members in contact with said fluid compositions, to functional fluid compositions which exhibit an improved tendency to resist fluid degradation and more particularly to compositions comprising certain functional fluids and an additive amount, suflicient to inhibit damage, of an ester compound.

Many different types of materials are utilized as functional fluids and functional fluids are used in many different types of applications. Thus, such fluids have been used as electronic coolants, atomic reactor coolants, ditfusion pump fluids, lubricants, damping fluids, bases for greases, power transmission and hydraulic fluids, heat transfer fluids, heat pump fluids, refrigeration equipment fluids and as filter mediums for air conditioning systems. In many of these uses there have been reports of damage to the fluid during use and to mechanical members, especially metallic members, in contact with the fluid as evidenced by a loss of weight of such members. Thus, damage had been reported in aircraft hydraulic systems, gas turbine bearings, jet turbine control systems, steam turbine bearings and steam turbine control systems. Damage has been observed on such materials as glass, Teflon, Mylar, Plexiglas and other members constructed from materials other than metals.

One particularly undesirable condition which exists during the use of a functional fluid and which can cause damage is cavitation, which can be described as a phenomenon which results in the formation and subsequent violent collapse of vapor-filled bubbles in a fluid subjected to requisite pressure changes. Bubbles can be formed when the fluid is at or below its bubble point pressure; above this pressure they collapse. Pressure changes suflicient to cause cavitation can occur in several ways; for example, a fluid flowing through a restriction, such as a partially closed valve, can encounter at the point of highest velocity a pressure far lower than both the bubble point and the valve outlet pressures. As the bubbles reach a point of high pressure, a violent collapse occurs thereby producing shock waves which can be severe enough to damage mechanical members in the fluid. As another example, cavitation conditions can occur when a surface is moved through or vibrated in a relatively stagnant liquid.

3,629,1l4 Patented Dec. 21, 1971 While there are many undesirable results caused by damage, One important aspect of the problem of damage is the eifect on hydraulic systems and fluids experiencing such damage. For example, the structural mechanical parts in a hydraulic system, such as pumps and valves, exhibits a marked decrease in strength, and the geometry of the parts is altered. Such changes in the case of pumps can cause a decrease in pumping efficiency and in the case of valves can cause faulty operations, excessive leakage or even hazardous conditions. As a result, damage necessitates premature overhaul of mechanical parts which is both costly and time consuming. In addition, as damage occurs the metal from metallic mechanical parts in contact with the functional fluid contaminates the fluids requiring premature draining of the fluids from the system, filter clogging and excessive filter replacement, and can cause a change in physical and chemical properties of the fluids. Also, metal contaminates can reduce the oxidative stability of a fluid thereby adversely affecting fluid performance. In addition to any effects resulting from contamination by metal (or other) contaminant, such damage to the fluid manifests itself in numerous ways, among which are (a) viscosity change, (b) increase in acid number, (c) formation of insoluble materials, ((1) increased chemical reactivity and (e) discoloration.

It is, therefore, an object of this invention to provide functional fluid compositions having an ability to inhibit and control damage.

It is a further object of this invention to provide func tional fluid compositions having an ability to inhibit and control damage and retain the desired properties of the functional fluid used to provide such compositions.

Further objects will be apparent from the following description of the invention.

It has now been found that damage, herein defined to include damage to a functional fluid and to mechanical members in contact with said fluid, can be effectively inhibited and controlled in the many functional fluid systems described by the incorporation of an ester compound into a functional fluid, said ester compound being represented by the structures (1) A monoester compound represented by the structure wherein R and R each can be alkyl, cycloalkyl, substituted alkyl, alkenyl, substituted alkenyl, aralkyl, substituted aralkyl, aryl and substituted aryl, each containing up to 10 carbon atoms, and

(2) Mixtures thereof;

(l) A diand triester compound represented by the structure ing up to 10 carbon atoms; and R can be a divalent hydrocarbon radical and a substituted hydrocarbon radical, and

(2) Mixtures thereof;

(1) A polyester compound represented by the structure wherein R is selected from the group consisting of hydrogen and alkyl, R and R are each selected from the group consisting of alkyl, substituted alkyl, cycloalkyl, aralkyl, aryl and substituted aryl, each containing up to 10 carbon atoms, a is a whole number having a value of 0 to 1, a is a whole number having a value of 0 to 1, Z is a whole number having a value of l to 4 and when Z is l a is O and R is selected from the group consisting of acyloxy and substituted acyloxy and when Z is 2 to 4 a is l and R is selected from the group consisting of acyl and acyl substituted by a number represented by R and (2) Mixtures thereof;

It is an important part of this invention that the incorporation of an ester compound in functional fluids produces a functional fluid composition having the ability to inhibit and control damage without adversely affecting the other properties of such fluids such as viscosity, oxidative and thermal stability, flash point, fire point, autogenous ignition temperature, corrosion resistance in the presence of metal parts and lubricating qualities of the functional fluid. In particular, it has been found that the viscosity of a base stock should not be altered materially by the incorporation of an additive since, in general, it has been found that a substantial decrease in viscosity can cause an increase in damage to the fluid and mechanical members in contact with said fluid. When the viscosity of the base stock is increased with respect to the additive which is incorporated into the fluid, it has been found that such increase in viscosity generally gives a slight reduction in the actual damage which can be caused by a functional fluid. Thus, it is generally preferred that the additive be incorporated into a base stock at a concentration such that it has no substantial effect on decreasing the viscosity of the base stock.

The functional fluids, to which an ester compound is added to provide the compositions of this invention, hereinafter referred to as base stocks, include, but are not limited to, esters and amides of an acid of phosphorus, mineral oil and synthetic hydrocarbon oil base stock, hydrocarbyl silicates, silicones and aromatic ether and thioether compounds. The concentration of an ester compound in the functional fluid is adjusted in terms of the particular system and the functional fluid which is utilized in this system to provide functional fluid compositions of this invention which contain additive amounts of an ester compound suflicient to inhibit and control damage while not adversely affecting other fluid properties. In particular, it has been found that the concentration of an ester compound utilized should be that amount of additive which will inhibit and control damage. In particular, it has been found that the additive response of a particular base stock, that is, the concentration of an ester compound which is sufficient to inhibit and control damage, varies according to the particular base stock.

In addition, it has been found that the concentration of an ester compound required to inhibit and control damage sometimes varies according to different species of base stocks which could be classified as a generic type of base stock. To illustrates the different additive response of species of a generic type base stock, it has been found that the additive response of a phosphate base stock will vary according to the type of phosphate base stock, that is, the concentration of an ester compound will vary according to whether the phosphate base stock is a trialkyl phosphate, a triaryl phosphate, a mixed alkylaryl phosphate or a mixture of the above phosphate base stocks. Thus, for esters of an acid of phosphorus the concentration of an ester compound suflicient to inhibit and control damage is from about 0.30 volume percent to about 15 volume percent, the particular concentration being that amount which will effectively inhibit and control damage. Since an ester compound is incorporated in a fluid at levels sufficient to inhibit damage and whereas fluid properties can be altered by the incorporation of any foreign element, it has generally been found that preferred additive concentrations of an ester compound for phosphate base stocks are from about 0.5 volume percent to about 9.0 volume percent, although 15 volume percent additive concentration is effective and contemplated within the scope of this invention. It is of particular importance that the additive be added to the phosphate base stock at a concentration which is suflicient to inhibit and control damage and which does not adversely affect other fluid properties, such as lowering the flash and fire points and causing a substantial decrease in viscosity. For amides of an acid of phosphorus, mineral oil and synthetic hydrocarbon oil base stocks, hydrocarbyl silicates, silicones and aromatic ether and thioether compounds, the concentration of an ester compound sufficient to inhibit and control damage is from about 0.15 volume percent to about 15 volume percent, the particular concentration being that amount which will effectively inhibit and control damage. Thus, it has been found that the concentration required to inhibit and control damage varies according to the particular base stock. The preferred additive concentration is from about 0.50 volume percent to about 12 volume percent of an ester compound, although 0.08 volume percent to about 15 volume percent have been found satisfactory and effective to inhibit and control damage.

Therefore, included within the present invention are compositions comprising a functional fluid and a damageinhibiting amount of an ester compound, that is, an ester compound is added, in a concentration sufficient to control and inhibit damage. The functional fluid compositions of this invention can be compounded in any manner known to those skilled in the art for the incorporation of an additive into a base stock as for example by adding an ester compound to the base stock with stirring until a homogeneous fluid composition is obtained.

Typical examples of monoester compound represented by (a) are methyl formate, ethyl formate, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, namyl acetate, isobutyl acetate, t-butyl acetate, isoamyl acetate, n-octyl acetate, methyl propionate, ethyl propionate, methyl n-butyrate, ethyl n-butyrate, isoamyl n-butyrate, methyl n-valerate, ethyl n-valerate, methyl isovalerate, isoamyl isovalerate, ethyl n-heptaylate, ethyl pelargonate, methyl benzoate, butyl benzoate, decyl benzoate, stearyl benzoate, benzyl acetate, benzyl propionate, benzyl valerate and benzyl pelargonate.

Typical examples of diester compounds which are represented by (b) can be prepared, for example, by the interaction of a dicarboxylic acid ester with an alcohol, by the interaction of a dihydroxy compound with an acid and by the interaction of a hydroxy carboxylic acid with a mixture of monohydric alcohols and monocarboxylic acids.

Typical aliphatic dicarboxylic acids where R, is alkylene are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, brassylic acid and thapsic acid, and where R is alkenylene are maleic acid, fumaric acid, glutaconic acid, citraconic acid, itaconic acid, ethidenemalonic acid, mesaconic acid, allylmalonic acid, allylsuccinic acid, teraconic acid, xeronic acid and cetylmalonic acid.

It is also contemplated herein to employ dimeric and trimeric polycarboxylic acids to produce the diand triester compounds represented by (b). When two like or unlike molecules of a polyethenoid monocarboxylicfatty acid condense to form a dicarboxylic acid, the product by definition is a dimer acid, or the carboxylic acid is said to be dimerized. In general, the dimer acids suitable for use in this invention are produced by the condensation of two like or unlike unsaturated aliphatic monocarboxylic acids having between about 16 and about 18 carbon atoms per molecule, examples of which comprise A -hexadecadienoic acid A -heptadecadienoic acid A -ctadecadienoic acid A -octadecadienoic acid A -octadecadienoic acid (linoleic acid) A -octadecadienoic acid A -octadecatrienoic acid A -octadecatrienoic acid (linolenic acid).

Typical dihydroxy compounds which can be used to prepare diester compounds represented by (b) are ethylene glycol,

1,2- or 1,3-propanediol,

1,2-, 1,3-, 1,4- or 2,3-butanediol, 1,3-, 1,4-, 1,1-, 2,3- or 2,4-pentanediol, 2-butene-1,2-di0l,

2-butene-1,4-diol, 2-brorno-1,3-propanediol, Z-methyl-1,5-pentanediol, 2,4-dimethyl-2,4-pentanediol, 1,1,l-trifiuoro-2,3-butanediol, 2,2-diethyl-1,4-butanediol, 2-pcntene-l,5-diol, 2-propyl-l,3-butanediol, 2-chloro-1,5-pentanediol, 1,4-hexanediol, -methyl-1,2-hexanediol,

2-ethyl- 1 ,3-hexanediol, 2-tert-bntyl-3,3,4,4-tetramethyl-1,Z-pentanediol, 4-methyl-l,4-hexanediol, 1,6-hexanediol, 3,3-dimethyl-1,6-hexanedio1, 2,4-dimethyl-3-hexene-2,5-diol,

2,3-, 2,4-, 2,5- or 3,4-hexanediol, 1,2,3,6-hexanetetrol, 2-heptene-l,6-diol, 5-ethyl-3-methyl-2,4-heptanediol, 1,2-, 1,3-, 1,4-, 1-8-, 2,4-, 2,7- or 4,5-octanediol, 2-methyl-2-octene-1,4-diol, 2,4,4,5,5,7-hexamethyl-3,6-octanediol, 2,7-dimethyl-4-octane-2,7-di0l, 2-butyl-4-ethyl-3-methyl-1,3-octanediol, 1,9-nonanediol,

1,2- or 1,10-decanediol,

1,2- or 1,12-dodecanediol, 5-decyne-4,7-diol, 5,9-dimethyl-8-decene-1,5-diol, 5,8-diethyl-6,7-dodecanediol, 9-octadecenel,l2-diol,

9,10- or 1,12-octadecanediol,

1,9- or 1,11-undecanediol, 1,13-tridecanediol, 1,2-tetradecanediol,

1,2- or 1,16-hexadecanediol, l6-mcthyl-1,2-heptadecanediol,

1,2- or 1,12-octadecanediol, iZ-methyl- 1 ,Z-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, propanediol,

6 2-isobutyl- 1,3 -propanediol, Z-ethyll ,3-butanediol, 2,2-diethyl-l,4-butanediol, 2,2,3,3-tetramethyl-1,4-butanediol, o-, mor p-xylene-a,a-diols, 3,6-dimethyl-o-xylene-a,u-diol, a,a'-dimethyl-p-xylene-a,a'diol, 1,6-diphenyl-l,6-hexanedio1, 1,2-diphenyl-1,2-ethanediol,

lor Z-phenyl-l,Z-propanediol, 2-methyi-l-phenyl-l,Z-prcpanediol, Z-di-o-tolymethyl-1,3-propanediol.

It is also contemplated Within the scope of this invention that trihydroxy compounds can be used, such as when one of the hydrogen atoms attached to a carbon atom of the above dihydroxy compound is replaced with a hydroxyl group.

Typical examples of aliphatic monocarboxylic acids which can be used to esterify the diand trihydroxy compounds as given above are as follows:

(a) ALIPHATI'C MONOCA-RBOXY'LI'C ACIDS (i) Where R and R each are alkyl or substituted alkyl Formic acid, acetic acid, fluoroacetic acid, propionic acid, fi-chloropropionic acid, butyric acid, isobutyric acid, nitroisobutyric acid, valeric acid, isovaleric acid, hexanoic acid, heptanoic acid, Z-ethylhexanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, undecanoic acid, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, eicosanoic acd, docosanoic acid and triacontanoic acid.

(ii) Where R and R each are an alkenyl or substituted alkenyl radical Butenic acid, pentenic acid, hexenic acid, teracrylic acid, hypogeic acid, oleic acid, elaidic acid, linoleic acid, a-eleostearic acid, fi-eleostearic acid, a-linolenic acid, acrylic acid, 5-chloroacrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, 3-butenoic acid, angelic acid, senecioic acid, hydrosorbic acid, sorbic and 4-tetradecenoic acid.

(b) ALICYCLIC MONOCARBOXY-LIC ACIDS Cyclopropanecarboxylic acid, cyclopentanecarboxylic acid, cyclohexanoic acid, hydrocarpic acid, chaulrnoogric acid, naphthenic acid, 2,3,4,5-tetrahydrobenzoic acid and cyclodecanecarboxylic acid.

(0) AROMATIC MONOCARBOXYLIC ACIDS Benzoic acid, l-naphthoic acid, Z-naphthoic acid, o-toluic acid, m-toluic acid, p-toluic acid, o-chlorobenzoic acid, m-chlorobenzoic acid, p-chlorobenzoic acid, 2,3-dibromobenzoic acid, 3,4-dichlorobenzoic acid, o-nitrogenzoic acid, m-nitrobenzoic acid, p-nitrobenzoic acid, 2,3-dinitrobenzoic acid, salicylic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, gallic acid, anisic acid, phenylacetic acid and ,B-phenylpropionic acid,

(d) HETEROCYCLIC MONOCARBOXYLIC ACIDS Picolinic acid, nicotinic acid, furylacrylic acid, piperic acid, indoxylic acid, 3-indoleacetic acid, cinchoninic acid, furoic acid, 2-thiophenecarboxylic acid, 2-pyrrolecarboxylic acid, 9-acridancarboxylic acid, quinaldic acid, pyrazionic acid and antipyric acid.

Typical examples of monohydric compounds which may be utilized to prepare ester compounds from diand tricarboxylic acids are methyl alcohol, ethyl alcohol, propyl alcohol, isopropyl alcohol, Z-ethylhexyl alcohol, dodecyl alcohol, 2,2-dimethyl heptanol, l-methylcyclohexyl methanol, n-butyl alcohol, hexanol, isohexanol, pentanol and mixtures of alcohols which are prepared by processes such as the 0x0 process. In addition, it is contemplated within the scope of this invention that the carboxylic acid groups of the above-illustrated monocarboxylic acids may be replaced by a hydroxyl group and these compounds may in turn be reacted with the diand tricarboxylic acids to prepare the diand triester compounds of this invention.

Typical diester compounds which are represented by (b) are di(2-ethylhexyl) azelate, di(2ethylhexyl) sebacate,

di-isooctyl sebacate,

Z-ethylhexyl 3:5:5 trmethylhexyl sebacate, di-isooctyl azelate,

di(3 :5 trimethylhexyl) sebacate,

di( l-methy1-4-ethy1octyl) sebacate, diisodecyl azelate,

diisotridecyl azelate,

di( l-methyl-4-ethyloctyl) glutarate, di(2-ethylhexyl) adipate, di(3-methylbutyl) azelate,

di( 3 5 5 trimethylhexyl) azelate, di(2-ethylhexyl) adipate,

di(C oxo) adipate,

bis(diethylene glycol monobutyl ether) adipate, di(isooctyl/isodecyl) adipate, diisotridecyl adipate,

triethylene glycol di(2-ethylhexanoate), hexanediol 1,6-di(2-ethylhexanoate) and dipropylene glycol dipelargonate.

Additional examples are mixtures of esters made from an aliphatic dibasic acid and a technical mixture of alcohols such as a mixture of alcohols obtained by the oxo process.

Typical polyester compounds represented by (c) can be prepared by the reaction of an acid compound with a polyhydroxy compound which polyhydroxy compound can be trimethylolpropane, trimethylolethane, pentaerythritol and dipentaerythritol. The acids which may be utilized are aliphatic monocarboxylic acids, alicyclic monocarboxylic acids, aromatic rnonocarboxylic acids and heterocyclic monocarboxylic acids, examples of which are given above. Examples of esters of this type are esters of trimethylolpropane (1 mole) with monocarboxylic acids (3 moles), e.g., trimethylolpropane tri-n-octanoate; esters of pentaerythritol (1 mole) with monocarboxylic acids (4 moles); esters of di or tripentaerythritol (1 mole) with monocarboxylic acids (6 or 8 moles).

The esters and amides of an acid of phosphorus which are suitable as base stocks for the functional fluid compositions of this invention are those represented by the structure wherein Y is selected from the group consisting of oxygen, sulfur and l iu N Y is selected from the group consisting of oxygen, sulfur and l n N Y is selected from the group consisting of oxygen, sulfur and fl nt N R R R R R and R each can be identical or different with respect to any other radical and b, c and d are whole numbers having a value of O to 1 and the sum of b+c+d is from 1 to 3.

Typical examples of alkyl radicals are as follows: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, secbutyl, tert-butyl, n-amyl, isoamyl, Z-methylbutyl, 2,2-dimethylpropyl, l-methylbutyl, diethylmethyl, 1,2-dimethylflint CnHal n l-mHmC (IIal) (l3 where Hal refers to a halogen, m is less than or equal to 2 and n may have any value from 0 to 18, and R and R can be hydrogen, halogen or alkyl radicals. Preferred radicals are those Where Hal is fiuoro and include those represented by the following formulas:

where R and R have their aforedescribed significance.

The halogenated alkyl radicals can be primary, secondary or tertiary.

Other suitable fluorine-containing radicals include fluorinated alkoxyalkyl radicals particularly those represented by the following formulas:

stituted aryl is partially or totally replaced by a halogen, 0-, mand p-trifluoromethylphenyl, o-, mand p-2,2,2-trifluoroethylphenyl, 0-, mand p-3,3,3-trifiuoropropylphenyl 0-, mand p-4,4,4-trifluorobutylphenyl.

The orthosilicates useful as base stocks include the tetraalkyl orthosilicates such as tetra(octyl)orthosilicate, tetra(2-ethylhexyl)orthosilicate and the tetra(isooctyl) orthosilicate and those in which the isooctyl radicals are obtained from isooctyl alcohol which is derived from the oxo process, and the (trialkoxysilicon)trialkyl orthosilicates, otherwise referred to as hexa(alkoxy) disiloxanes, such hexa(2-ethylbutoxy) disiloxane and hexa (Z-ethylhexoxy) disiloxane.

The preferred tetraalkyl orthosilicates and hexa(alkoxy) disiloxanes are those in which the alkyl or alkoxy radicals have from 4 to 12 carbon atoms and in which the total number of carbon atoms in the orthosilicate is from 16 to 60.

In addition to the hexa(alkoxy) disiloxanes referred to above, other hexa(alkoxy) disiloxanes can be used in which the aliphatic radical of the alkoxy groups are for example, l-ethylpropyl, 1,3-dimethylbutyl, Z-methylpentyl, l-methylhexyl, l-ethylpentyl, Z-butylhexyl and 1-methyl-4- ethyloctyl.

The orthosilicates and alkoxy polysiloxanes can be represented by the general structure wherein R R and R each can be alkyl, substituted alkyl, aryl, substituted aryl and can be identical or different with respect to any other radical, O is oxygen, Si is silicon, X is a member of the group consisting of carbon and silicon, in is a whole number having a value of O or 1, n is an integer having a value of from 1 to about 200 or more and when X is carbon in is O, n is 1 and R R and R each can be hydrogen, alkyl, substituted alkyl, aryl and substituted aryl radicals and when X is silicon in is 1, n is an integer having a value of from 1 to about 200 or more and R R and R each can be alkyl, substituted alkyl, aryl and substituted aryl.

Typical examples of substituted aryl radicals are 0-, mand p-chlorophenyl, o-, mand p-bromophenyl, o-, mand p-fluorophenyl, a,a,a-trichlorocresyl, 0t,ot,zx-lllfill0l0 cresyl, xylyl and o-, mand p-cresyl. Typical examples of alkyl and haloalkyl radicals are those heretofore described.

The organopolysiloxanes useful as base stocks are represented by the general structure wherein R R R R R and R can each be alkyl, substituted alkyl, aryl and substituted aryl radicals and need not represent the same entity throughout the same molecule and n is a whole number from about 0 to about 2000 or more. Typical examples of alkyl and haloalkyl radicals are those heretofore described. Typical examples of the organopolysiloxanes are dimethylpolysiloxane, methyl-phenyl polysiloxane, methylchlorophenyl polysiloxane and methyl-3,3,3-trifiuoropropy1 polysiloxane.

Typical examples of substituted aryl radicals and o-, mand p-chlorophenyl, o-, mand p-bromophenyl, o-, mand p-fiuorophenyl, a,a,ot-trichlorocresyl, a,a,a-trifluorocresyl, omand p-cresyl and xylyl.

1 1 Another class of base stocks which are suitable as base stocks for this invention are represented by the structure wherein A, A A and A are each a chalkogen having an atomic number of 8 to 16, X, X X X and X each are selected from the group consisting of hydrogen, alkyl, haloalkyl, halogen, arylalkyl and substituted arylalkyl, x, y and z are whole numbers each having a value of to 8 and e is a whole number having a value of 0 to 1 provided that when e is 0, y can have a value of 1 to 2. Typical examples of alkyl and substituted al kyl radicals are given above. Typical examples of such base stocks are 2- to 7-ring ortho-, metaand para-polyphenyl ethers and mixtures thereof, 2- to 7-ring ortho-, metaand para-polyphenyl thioethers and mixtures thereof, mixed polyphenyl ether-thioether compounds in which at least one of the chalkogens represented by A, A A and A is dissimilar with respect to any one of the other chalkogens, dihalogenated diphenyl ethers, such as 4-bromo-3'-chlorodiphenyl ethers and bisphenoxybiphenyl compounds and mixtures thereof.

Examples of the polyphenyl ethers contemplated are the bis(phenoxyphenyl) ethers, e.g., bis(m-phenoxyphenyl) ether, the bis(phenoxyphenoxy)benzenes, e.g., mbis(m-phenoxyphenoxy)-benzene, m bis(p-phenoxyphenoxy)benzene, o-bis(o-phenoxyphenoxy)benzene, the bis (phenoxyphenoxyphenyl) ethers, e.g., bis[m-(m-phenoxyphenoxy)phenyl] ether, bis[p (p phenoxyphenoxy) phenyl] ether, m-[(m-phenoxyphenoxy) (o-phenoxyphenoxy)] ether and the bis(phenoxyphenoxyphenoxy)benzenes, e.g., m-bis[m-(m-phenoxyphenoxy)phenoxy]benzene, p-bis[p-(m-phenoxyphenoxy)phenoxy]benzene, mbis [m- (p-phenoxyphenoxy) phenoxy] benzene and mixtures thereof with other polyphenyl ethers.

Typical examples of polyphenyl thioethers and mixed polyphenyl ethers and thioethers are 2-phenylmercapto-4'-phenoxydiphenyl sulfide,

2-phenoxy-3-phenylmercaptodiphenyl sulfide,

o-bis (phenylmercapto benzene,

phenylmercaptobiphenyl,

bis (phenylmercapto biphenyl,

m- (m-chlorophenylmerc apto -m-phenylrnercaptobenzene,

phenylmercaptotphenoxy) biphenyl,

m-chlorodiphenyl sulfide,

bis(o-phenylmercaptophenyl) sulfide,

m-bis (m-phenylmercaptophenylmercapto benzene,

1,2, 3-tris (phenylmercapto benzene,

1-phenylmercapto-2,3-bis (phenoxy benzene,

o-bis (o-phenylmercaptophenylmercapto benzene,

m-bis (p-phenylmercaptophenylmercapto benzene,

2,2'-bis (phenylmercapto diphenyl ether,

3 ,4'-bis (m-tolylmercapto diphenyl ether,

3 ,3 '-bis (xylylmercapto diphenyl ether,

3 ,4-bis m-isopropylphenylmercapto -dipheny1 ether,

3 ,4'-bis (p-tert-butylphenylmercapto diphenyl ether,

3 ,3 -bis (m-chlo rophenylmercapto diphenyl ether,

3,3-bis(m-trifiuoromethylphenylmercapto)diphenyl ether,

3 ,4-bis m-perfluorobutylphenylmercapto diphenyl ether,

2-m-tolyloxy-2'-phenylmerca ptodiphenyl sulfide,

o-bis phenylmercapto) benzene,

bis(m-phenylmercaptophenyl) sulfide,

m-phenylmercaptophenyl-p-phenylmercaptophenyl sul fide,

the trisphenylmercaptobenzenes such as 1,2,4-trisphenylmercaptobenzene,

3,3 -bis phenylmercapto -biphenyl,

m-bis p-phenylmercaptophenylmercapto benzene,

m-bis (m-phenylmercaptophenylmercapto benzene,

bis [m- (m-phenylmercaptophenylmercapto phenyl] sulfide,

3 ,3 -bis phenylmerc apto diphenyl ether,

3,3-bis (phenoxy) diphenyl sulfide,

3-phenoxy-3-phenylmercaptodiphenyl sulfide,

3-phenylmercapto-3'-phenoxydiphenyl ether,

3 ,4-bis (phenylmercapto diphenyl ether,

m-bis (m-phenylmercaptophenoxy benzene,

3 -phe11ylmercapto-3 (m-phenylmercaptophenylrnercapto diphenyl ether.

Other base stocks which are useful are monoand dialkylthiophenes. Typical examples of thiophenes are 2,5 l-hexyll-methylnonyl) thiophene,

2,4-( l-hexyll-methylnonyl)thiophene, 2-tert-buty1 thiophene,

2,5-tert-butyl thiophene, 2,5-(1,1-dimethylpropyl)thiophene,

2,5 l-butyl-l-octylnonyl thiophene, 2,5-( l-propylcyclobutyl) thiophene, 2-tert-butyl-4-( l-octyll-methyloctadecyl thiophene, 2,5-( l-methylcyclohexyl) -thiophene, 2,5-( l-octyl-l-methyldecyl)thiophene, 2,5-( 1,1-dimethyltridecyl) thiophene, 2,3-(l,1-dimethyltridecyl)thiophene, 2,4-(1,1-dimethyltridecyl)thiophene, 2,4-( l-methylcyclopentyl -thiophene and 2,4-( l-n-dodecylpentyl thiophene.

Hydrocarbon oils including mineral oils derived from petroleum sources and synthetic hydrocarbon oils are suitable base stocks. The physical characteristics of functional fluids derived from a mineral oil are selected on the basis of the requirements of the fluid systems and therefore this invention includes as base stocks mineral oils having a wide range of viscosities and volatilities such as naphthenic base, paraffinic base and mixed base mineral oils. In addition, lower boiling hydrocarbon oils such as fuel oil and kerosene types are often pumped at pressures whereby pump surfaces can be damaged, such as the pumping of jet fuels, and these fuels are included within the term hydrocarbon oils.

The synthetic hydrocarbon oils include but are not limited to those oils derived from oligomerization of olefins such as polybutenes and oils derived from high alpha olefins of from 8 to 20 carbon atoms by acid catalyzed dimerization and by oligomerization using trialuminum alkyls as catalysts.

It is also contemplated within the scope of this invention that mixtures of two or more of the aforedescribed base stocks can be utilized as base stocks.

The invention can be better appreciated by the following non-limiting examples. In Examples 1 through 31 a nickel specimen was immersed in the fluid and a 20 kilohertz vibration induced into the specimen. The test duration was 45 minutes. In all the following examples, the temperature during the test was C. except where so indicated by the asterisk Relative weight loss is defined to mean the total Weight loss of the metal specimen when tested in the fluid containing the additive present divided by the weight loss of the metal specimen when the fluid is tested without any additive present times 100. Thus, a relative weight loss under indicates that less metal was removed from the specimen when the additive was present in a given base stock and therefore demonstrates that the fluid compositions which incorporate an ester compound of this invention inhibit and control damage.

TABLE I Volume percent Relative I additive weight No. Fluid composition Additlvo i flu l 1 Tributyl phosphate Dioctyl sebacate- 93 ..-..do Butyl benzoate 5 86 Dipentaerythritol es 5 91 Butyl stearate 5 86 Ethyl acetate. 5 59 sphate... Diethylsuecinat 5 83 Dipentaeiythritol es 5 90 Ethyl acetate 5 72 Dipentaerythritol ester. 5 88 Ethyl aeetate 5 83 cresyl phosphate Dioctyl sebacate. 5 80 Diethyl succinate--. 5 79 Dipentaerythritol es en... 5 89 Pentaerythritol tetravalera e.- 5 89 Ethyl aeetate 5 71 5 60 Dioctyl sebacate 5 88 rethylsuccmate 5 91 Ethyl acetate- 5 75 hyl Diethyl succinate 5 88 8Z$5% dilbudtsrlphenyl phosphate 0 acry o1 improver 1% epoxidized soybean oil Dmctyl Sebacate 5 95 .50% bis(1,2-phenylmercapto) ethane il5l7 ;6% dilbuylphenyl phosphate 0 acry 01 improver 22 epoxidized Soybean l Dlethyl Succlnate 5 92 50% bis(1,2-phenylmercapto) ethane"... 875% dilbudtylrfhenyl phosphate 11 0 acry oi improver 1% epoxidized soybean oil Ethyl acetate 5 36 50% bis(1,2-phenylmcrcapto) ethane... 87 .71 5% dilbngyll lihenyl phosphate. 11 0 aory oi improver 1% epoxidized soybean oil Phenylproplonate 5 86 50% bis(1,2-phenylmercapto) ethane. 835% dilbnygphenyl phosphate...

0 acry 01 improver 25. 1% epoxidized soybean oil Pentaerythntol tetravalerate 2 91 .7550;%3bi%(11,2-rlhe)nylmeeagto) iatliiirlnov 0 -c ororomo 1p eny e erl 3-chlorodipheny] ether }Dlethyl Succlnate 5 95 i7 ti ih fl fi r '11 i; t

. 2-e y exy ip cny p osp a e-- 47.8% isooctyldiphenyl phosphatc Dloetyl sebacate 5 89 10 ppm. silicone 28. N -methyl-N-buty1-N-methyl-N -butyl p- Diethyl succinate 5 91 phosphorodiamidate. 29..-" Mineral Oil Dioctyl sebacate 5 78 30.... ..do Diethyl succinate 5 87 87.15% dibutylphenyl phosphate. 31..... 11% acryloid VI improver 6,000 Molecular weight polymer prepared from adipic acid and 2 87 1% epoxidized soybean oil 1,2-propane diol. 50% bis(1,2-phenylmercapto) ethane 1 Refers to experimental runs which were made at a temperature of 30 C.

It is an important part of this invention that the use of an ester compound controls and inhibits fluid damage. Several methods which are used to determine the degree of fluid degradation or the change in optical absorbence of a fluid after being subjected to an ultrasonic vibration. In addition, the physical properties, such as viscosity increase and acid number increase, of the fluid are determined prior to and after a given run. In Table II the outstanding ability of the functional fluid compositions of this invention are demonstrated with regard to inhibiting and controlling fluid damage. In Table II the relative inhibition of fluid degradation as determined by optical absorbence was obtained by dividing the optical absorbence of the fluid compositions with additives by the optical absorbence of fluid compositions without additives times 100. The relative decrease in acid number build-up was obtained by dividing the acid number of the fluid compositions with additives by the acid number of fluid compositions without additives times 100. In all of the following examples the runs with and without additives were at the same temperatures and for the same duration.

The test method as employed to determine relative damage has been found to correlate quite well to actual test runs on simulated hydraulic system test stands, such as the Fairey Test Stand. The Fairey Test Stand is a closed loop hydraulic system wherein the test conditions simulate the actual fluid pressures and temperatures as could exist on an aircraft. Such test stand has been in use for the purpose of testing hydraulic fluids and hydraulic components. In addition, the hydraulic system test stands for determining damage have correlated quite Well with the hydraulic system of commercial aircraft where damage levels have been determined.

The data in the previous examples demonstrate the significant inhibition of damage obtained by the incorporation of an ester compound into a base stock. In addition, the physical properties and the performance characteristics such as lubricity, fire resistance, and viscosity were essentially unaffected by the additive, an important consideration since a base stock is selected trom a given fluid system because of its physical properties or characteristics and deviations from these prop- TABLE II Concen- Relative tration, optical Relative Ex. volume absorbacid N 0. Base stock Additive percent ence number 32 87.15% dibutylphenyl phosphate.. Ethyl acetate 5 33 .do Diethyl succinate. 5 34.. .d0 Dipentaerythritol ester, 5 35 Tricresyl phosphate Dioctyl sebacate. 5 36 do Ethyl acetate. 5 37.. do. Diethyl succinate.. 5 38 do. Dipentaerythritol ester... 5 39 do Pentaerythritol tetravalerate. 5

erties and characteristics can bring about inferior fluid performance.

As is demonstrated by Table I, the ester compounds are effective in inhibiting and controlling damage to mechanical members in contact with such fluids which contain the ester compounds of this invention. It is of particular importance that the inhibition and control of damage is accomplished without adversely affecting any of the critical properties of the functional fluids.

The effectiveness of the ester compounds for inhibiting and controlling the degradation of the base stocks is well illustrated by Table II. In particular Table II effectively demonstrates that the ester compounds at low concentrations are effective in preventing degradation of the base stock as is evidenced by the relative decrease in optical absorptivity and acid number of the fluid. This inhibition of degradation of the base stock is of particular importance in the many uses of functional fluids wherein the original required fluid characteristics are maintained during use by the incorporation of the ester compounds. Thus, the incorporation of an ester compound into a base stock to inhibit and control fluid damage is of particular importance in that fluid damage manifests itself in numerous ways among which are viscosity change, increase in acid number, formation of insoluble materials, increased reactivity and discoloration. In a fluid system the particular properties of a fluid have to be maintained in order to continue useful operation of the particular system in which the fluids are employed. Thus, changes in viscosity can be produced by fluid degradation whereby polymeric products with high molecular weights are produced in the system. Such high molecular weight products often become insoluble in the particular base stock which results in the precipitation or sludging of the insoluble material. Such precipitation and sludging plugs filters and deposits on moving parts which have to be lubricated by the fluid thereby causing inadequate lubrication and interference with the proper functioning of the mechanical parts. Increased chemical reactivity is observed on fluid degradation as well as buildup in acid number of the fluid. Such increased chemical reactivity and high acid number allows the particular system which incorporates the fluid to be chemically attacked by the fluid thereby causing pitting, wear and alterations of the close tolerances of the mechaniical members of said fluid. Thus, premature overhall of mechanical parts is a direct consequence of fluid degradation. It is, therefore, of particular importance that fluid degradation is controlled and inhibited so as to extend the useful life of a fluid in a functional fluid system.

As a result of the excellent inhibition and control of damage utilizing the functional fluid compositions within the scope of this invention, improved hydraulic pressure devices can be prepared in accordance with this invention which comprise in combination a fluid chamber and an actuating fluid composition in said chamber, said fluid comprising a mixture of one or more of the base stocks hereinbefore described and a minor amount, suflicient to inhibit damage, of an ester compound. In such a system, the parts which are so lubricated include the frictional surfaces of the source of power, namely the pump, valves, operating pistons and cylinders, fluid motors, and in some cases, for machine tools, the ways, tables and slides. The hydraulic system may be of either the constant-volume or the variable volume type of system.

The pumps may be of various types, including centrifugal pumps, jet pumps, turbine vane, liquid piston gas compressors, piston-type pump. more particularly the variable-stroke piston pump, the variable-discharge or variable displacement piston pump, radial-piston pump, axial-piston pump, in which a pivoted cylinder block is adjusted at various angles with the piston assembly, for example, the Vickers Axial-Piston Pump, or in which the mechanism which drives the pistons is set at an angle adjustable with the cylinder block; gear-type pump, which may be spur, helical or herringbone gears, variations of internal gears, or a screw pump; or vane pumps. The valves may be stop valves, reversing valves, pilot valves, throttling valves, sequence valves, relief valves, servo valves, non-return valves, poppet valves or unloading valves. Fluid motors are usually constantor variabledischar e piston pumps caused to rotate by the pressure of the hydraulic fluid of the system with the power supplied by the pump power source. Such a hydraulic motor may be used in connection with a variable-discharge pump to form a variable-speed transmission. It is, therefore, especially important that the frictional parts of the fluid system which are lubricated by the functional fluid be protected from damage. Thus, damage brings about seizure of frictional parts, excessive wear and premature replacement of parts.

The fluid compositions of this invention when utilized as a functional fluid can also contain dyes, pour point depressants, metal deactivator, acid scavengers, antioxidants, defoamers in concentration sufficient to impart antifoam properties, such as from about 10 to about parts per million, viscosity index improver such as polyalkylacrylates, polyalkylmethacrylates, polycyclic polymers, polyurethanes, polyalkylene oxides and lubricity agents and the like.

It is also contemplated within the scope of this invention that the base stocks as aforedescribed can be utilized singly or as a fluid composition containing two or more base stocks in varying proportions. The base stocks can also contain other fluids which include, in addition to the functional fluids described above, fluids derived from coal products, and synthetic oils, e.g., alkylene polymers (such as polymers of propylene, butylene, etc., and the mixtures thereof), alkylene oxide-type polymers (e.g., propylene oxide polymers) and derivatives, including alkylene oxide polymers prepared by polymerizing the alkylene oxide in the presence of water or alcohols, e.g.. ethyl alcohol, alkyl benzenes (e.g., monoalkyl benzene such as dodecyl benzene, tetradecyl benzene, etc.), and dialkyl benzene (e.g., n-nonyl Z-ethylhexylbenzene); polyphenyls (e.g., biphenyls and terphenyls), halogenated benzenes, for example, fluoro-, bromoand chloro-benzenes such as mdibromobenzene, p-dichlorobenzene, etc. halogenated lower alkyl benzene, for example, bromo and chloro substituted lower alkyl benzenes such as trichloromethyl benzene, bromomethylbenzene, etc. halogenated biphenyl, for example, chlorinated biphenyl having by weight from about 21% to 60% of combined chlorine, etc. and mono halogenated diphenyl ethers, for example, p-chlorophenylphenyl ether, p-bromo-phenylphenyl ether, meta-cholorophenylphenyl ether etc.

While this invention has been described with respect to various specific examples and embodiments, it is to be understood that the invention is not limited thereto and that it can be variously practiced within the scope of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A composition comprising (A) a major amount of a base stock comprising liquid esters of an acid of phosphorus selected from the class consisting of triaryl phosphates, trialkyl phosphates, mixed aryl-alkyl phosphates and mixtures thereof, wherein the total number of carbon atoms present in each alkyl group is from 1 to 18 carbon atoms and in each aryl group is from 6 to 10 carbon atoms, and

(B) a damage inhibiting amount of a monoester compound represcnted by the structure ll R-C-O-R wherein R and R each are an alkyl, haloillkyl, allienyl or aryl group containing up to 10 carbon atoms and mixtures thereof.

2. A composition of claim 1 wherein the base stock is dibutylphenyl phosphate and the monoester is ethyl acetate.

3. A composition of claim 1 wherein the base stock is tributyl phosphate and the monoester is ethyl acetate.

4. A composition of claim 1 wherein the base stock is a mixture of tributyl phosphate and tricresyl phosphate and the monoester is ethyl acetate.

5. A composition of claim 1 wherein the base stock is tricresyl phosphate and the monoester is ethyl acetate.

6. A composition of claim 1 wherein the base stock comprises above 89% by volume of the total fluid composition.

7. In the method of operating a hydraulic pressure device wherein a displacing force is transmitted to a displaceable member by means of a hydraulic fluid, the improvement which comprises employing as said fluid a composition of claim 1.

8. In the method of operating. a hydraulic pressure device wherein a displacing force is transmitted to a displaceable member by means of a hydraulic fluid, the improvement which comprises employing as said fluid a composition of claim 6.

9. A process for controlling cavitation damage in a hydraulic system which is subject to cavitation damage when operated using a force transmission fluid comprising a major amount of a base stock selected from the group consisting of triaryl phosphates, trialkyl phos phates, mixed aryl-alkyl phosphates and mixtures thereof, wherein the total number of carbon atoms present in each alkyl group is from 1 to 18 carbon atoms and in each aryl group is from 6 to 10 carbon atoms which comprises using as the force transmission fluid a major amount of such base stock and from 0.5 to 15 volume percent of a monoester compound represented by the structure R("]OR1 wherein R and R each are an alkyl group, a haloalkyl, an alkenyl, or an aryl group containing up to 10 carbon atoms and mixtures thereof.

10. A process of claim 9 wherein the hydraulic system is an aircraft hydraulic system.

References Cited UNITED STATES PATENTS 2,175,877 10/1939 Clark 25249.9 2,241,531 5/1941 Wiezevich 252-49.8 2,340,073 1/1944 Morgan 25256 X 2,889,354 5/1959 Blake et al. 252-56 2,933,449 4/1960 Moreton 25249.9 2,698,837 1/1955 Gamrath et al. 252-78 OTHER REFERENCES Bushe: Causes of Failure of Diesel Crankshaft Bearings, Chem. Abs, vol. 53 (1959), p. 18811.

Bull; Tensile Strengths of Viscous Liquids Under Dynamic Loading, Chem. Abs., vol. 51 (1957), pp. 4085-4086.

PATRICK P. GARVIN, Primary Examiner W. H. CANNON, Assistant Examiner US. Cl. X.R. 

